This invention relates generally to electronic circuits generally, and more particularly the invention relates to analog electronic circuits.
Analog circuits typically operate on linear or analog signals which represent real world phenomenon such as temperature, pressure, and sound and are continuously variable over a wide range of values. This is to be distinguished from digital signals which represent the "ones" and "zeros" of binary arithmetic.
In temperature sensor products, for example, a signal proportional to absolute temperature (PTAT) and a signal complimentary to absolute temperature (CTAT) are obtained and manipulated. The PTAT signal, or current, is generally developed by applying the voltage difference of two bipolar junctions (transistors or diodes) running at different current density across a resistor. The current through the bipolar junctions should be constant or exponential in temperature. The CTAT current is developed by applying the voltage from a single bipolar junction (transistor or diode) across a resistor.
The junction voltage of a bipolar diode or transistor, whose current is constant or an exponential function of temperature is almost linear in temperature. The non-linear portion of the temperature function is called the curvature. This negative linear temperature coefficient is useful in band gap references, temperature sensors and other products. In most cases, a strictly linear response with curvature canceled would be optimal.
The present invention is directed to canceling the curvature in the temperature function of a bipolar junction base-emitter voltage.